Electroluminescent device utilizing interconnected electrically conductive particles within a dielectric medium



Oct. 28, 1969 1. LlTANT-ETAL 3,475,640

ELECTROLUMINESCENT DEVICE UTILIZING INTERCONNECTED ELECTRICALLY CONDUCTIVE PARTICLES WITHIN A DIELECTRIC MEDIUM Filed Aug. 19, 1965 2 Sheets-Sheet 1 MEANS POWER SUPPLY r MEANS INVENTORS IRVING LITANT RALPH C. PRATT GERALD L. ALLEN ATTOR (EYS Oct. 28, 1969 l. LITANT ETA 3,475,640

ELECTROLUMINESCENT DEVICE UTILIZI INTERCONNECTED ELECTHICALLY CONDUCTIVE PARTICLES WITHIN A DIELECTRIC MEDIUM Filed Aug. 19, 1965 2 Sheets-Sheet 2 ov |5ov INVENTORS IRVING L NT PH c. TT

ALD L. ALLEN Arr-0mg YS United States Patent ELECTROLUMINESCENT DEVICE UTILIZING INTERCONNECTED ELECTRICALLY CON- DUCTIVE PARTICLES WITHIN A DIELEC- TRIC MEDIUM Irving Litant, Lexington, Ralph C. Pratt, Maynard, and Gerald L. Allen, Wilmington, Mass., assignors to Avco Corporation, Cincinnati, Ohio, a corporation of Delaware Filed Aug. 19, 1965, Ser. No. 480,978 Int. Cl. H01j 1/62, 63/04 US. Cl. 313-108 3 Claims ABSTRACT OF THE DISCLOSURE This invention relates to electroluminescent devices and, more particularly, to electroluminescent devices using a plurality of electrical conducting paths within a dielectric matrix.

The phenomonon of electroluminescence has been studied for many years, and electroluminescent devices are marketed commercially. Typically, an electroluminescent device comprises a pair of spaced electrodes at least one of which is transparent. A quantity of electroluminescent phosphor, that is, material which emits a visible light when placed within an electric field, is inserted between the spaced electrodes. Upon the application of an alternating potential difference between the electrodes, the phosphor emits visible light.

It is an object of the invention to provide an electroluminescent device which is structurally novel and, more particularly, which (1) includes multiple electrical conducting paths; and (2) includes a dispersion of phosphor disposed in a spaced relationship with the electrical conducting paths.

It is another object of the invention to provide an electroluminescent device which may be manufactured in a simple and facile manner and, more particularly, in a substantially single-step potting technique.

It is still another object of the invention to provide an electroluminescent device which may be made fully flexible, fully transluscent.

It is still another object of the invention to provide an electroluminescent device with radically reduced spacing between electrical conducting media.

Other objects of the invention are to provide an electroluminescent device which provides (1) a mixture of electrical conducting means and phosphor in a dielectric medium; (2) compatibility with many prior art approaches of constructing electroluminescent devices; (3) filamentary or particle electrodes in place of area electrodes; (4) a three-dimensional electric field; (5) a structure without an electrode as this term is conventionally understood to mean.

In accordance with the invention, an electroluminescent device comprises a pair of spaced, electrically conducting paths, each path comprising a dispersion of electrically conducting particles within a dielectric medium. The electroluminescent device also includes electroluminescent phosphors disposed in the space between electrically conducting paths.

The novel features that are considered characteristic of the invention are set forth in the appended claims; the invention itself, however, both as to its organization and method of operation, together with additional objects and advantages thereof, will best be understood from the following description of a specific embodiment when read in conjunction with the accompanying drawings, in which:

FIGURE 1 is a schematic representation of one form of an electroluminescent device embodying the principles of the present invention;

FIGURE 2 depicts an alternate embodiment of the lnvention;

FIGURE 3 is a schematic representation useful in explaining the principles of operation;

FIGURE 4 depicts a section taken along lines 44 in FIGURE 3;

FIGURE 5 depicts a section taken along 5-5 in FIG- URE 3; and

FIGURE 6 illustrates a third form of the invention wherein an electrically conducting fabric is used.

Referring to FIGURE 1, there is depicted one embodiment of the invention. Specifically, numeral 10 applies to an electroluminescent device comprising a dielectric panel 11 which is preferably transparent and preferably formed from a plastic material such as epoxy resin. In the alternative, the panel 11 may be formed from polyvinyl chloride, polyurethane resin systems and of any suitable material compatible with the components to be combined therewith.

In addition, the panel 11 contains dispersed therein, preferably in a purely random fashion, electrical conducting fibers 12. For best results, these fibers 12 are carbonaceous-that is, formed from a carbonaceous or a graphite material. In practice, the fiber content of the panel is less than one percent by weight and, under these conditions, a transparent panel 11 retains its transparent qualities. Electrical conducting flakes or particles will also function in this type of device where a potential difference can be established between the particles and flakes.

The panel 11 also contains dispersed therein in a purely random fashion electroluminescent phosphor material 13 which is preferably in fine powder form. Electroluminescent phosphor material may be any one of the widely used materials such as zinc sulfide containing well-known contaminants which enhance its phosphorescence.

By way of a schematic representation, a pair of electrodes 14 and 16 are shown connected to the panel 11 and, more particularly, in electrical contact with the electrical conducting fibers 12. Again, schematically, the electrodes 14 and 16 are coupled to a source of electric power 17 which supplies a potential difference between the electrodes 14 and 16.

Referring to FIGURE 3 of the drawings, there is contained an oversimplified schematic representation of a pair of electrical conducting paths 31 and 32 formed by carbonaceous fibers through a dielectric matrix 33. Each path traverses the distance between a pair of electrodes 34 and 36 across which is assumed there exists a potential difference of volts from power supply means 30.

Path 31 comprises ten series interconnected filaments and, assuming uniform diameters of the filament and uniform lengths between filament junctions, a uniform voltage distribution will result. The potential with respect to electrode 34 of each junction is indicated by the underlined values.

Path 32 is made up of fifteen series-connected filaments and, again assuming uniform filament diameters and uniform distances between filament junctions, the

potential difference with respect to electrode 34 of each junction is shown in the circles.

Although the fibers in paths 31 and 32 appear to be touching at numerous places, they may or may not be in contact. It will be seen particularly from FIGURES 4 and 5 representing sections 44 and 5-5 of FIGURE 3 that the filaments 38 and 40, as well as filaments 42, 44, 46 and 48 are in fact spaced. In short, there is a three-dimensional distribution throughout the dielectric panel 33. In fact, referring to FIGURES 1 or 2, there are numerous electrical paths forms of a highly complex nature.

Another purpose of FIGURE 3 is to show that the random meandering of the various electrical paths will create potential differences between adjacent conducting element (filament) between each separate and distinct pair of electrical conducting paths, more particularly between adjacent conducting elements between which there exists a potential difference. It is quite obvious that where a potential difference exists between spaced conductors there is formed an electrical field. The magnitude of this field is proportional to the potential difference and inversely proportional to the distance separating the adjacent fibers. Assuming a five-volt difference between the fibers 38 and 40 shown in FIGURES 1 and 3 and further assuming a five-mil (0.005) separation between these fibers, there exists an electric field of 5,000 volts per inch. This is more than enough to cause an electroluminescent particle spaced between these particles to luminesce or produce light.

Thus, the panel depicted in FIGURE 1 provides an unusual, singularly novel electroluminescent device wherein electrical conducting means and electroluminescent particles are intermittently mixed in a dielectric panel. There are created a volumetric distribution of electric field and volumetric or three-dimensional distribution of light caused by particles disposed within these electric fields.

Of particular significance in addition to the novel electrical and electroluminescent properties discussed above is the fact that using electrically conducting carbonaceous elements, a relatively small amount of fibers is required to form the necessary electrical conducting paths. Accordingly, the optical properties of the matrix material are maintained substantially intact. The physical properties of the matrix material are not affected, so that a flexible matrix material remains flexible. Referring to FIGURE 2, an alternate construction of an electroluminescent device embodying the principles of of the present invention is shown. This particular electroluminescent device 18 comprises a preferably transparent matrix dielectric material 19 containing electroluminescent phosphor 21 sandwiched between a pair of electrodes 22 and 23. The electrodes 22 and 23 in this case comprise a dielectric material 24 containing electrical conducting fibers 26, preferably carbonaceous fibers as described above, The electrodes 22 and 23 are coupled through a pair of terminals 27 and 28 respectively to a source of electrical power and potential difference 29.

The filaments in panels 23 and 24 are used to provide transparent or translucent electrodes between which is sandwiched phosphorous material and across which can be applied an electrical potential. The interesting aspect of this particular construction is that the electrode material may now be selected because of the properties of the matrix material from which it is formed. There is no longer a dependency on the use of a metal substrate or a relatively transparent metal oxide electrical conducting coating. It should be emphasized that in the FIGURE 3 construction, the interconnected filamentary conductors represent equal potential surfaces and thus simulate a planar electrical conductor. These filaments accomplish this result without substantially affecting the properties of the matrix materials of the panels 23 and 24.

The illustration in FIGURE 6 shows a fragment of a third type of construction embodying the present invention. A dielectric body has dispersed therein spaced openweave, electrically conducting fabrics such as 51, 52 (in dotted outline) and 53. Electroluminescent phosphors 54 are dispersed throughout the dielectric medium between the fabric and in openings of the fabric. Upon establishing a suitable potential difference between fabrics and thus an electric field between said fabrics 51, 52 and 53, light will be emitted by the phosphors 54. Unusual decorative effects are possible.

If the openings in the fabric are small, it may be necessary to align the openings to permit light to pass through the dielectric material. In the event fabric with large openings is used, the fabrics may be positioned in a random fashion.

The various features and advantages of the invention are thought to be clear from the foregoing description. Various other features and advantages not specifically enumerated will undoubtedly occur to those versed in the art, as likewise will many variations and modifications of the preferred embodiment illustrated, all of which may be achieved without departing from the spirit and scope of the invention as defined by the following claims.

We claim:

1. An electroluminescent article including a pair of spaced electrodes comprising at least a pair of electrically conducting paths forming continuous current paths between said electrodes, each path comprising a dispersion of interconnecting electrically conducting particles within a dielectric medium; and electroluminescent phosphors dispersed in the dielectric medium in the space between electrically conducting paths.

2. An electroluminescent article including a pair of spaced electrodes comprising at least a pair of electrically conducting paths forming continuous current paths between said electrodes, each path comprising a dispersion of interconnecting electrically conducting filaments within a dielectric medium; and electroluminescent phosphors dispersed in the dielectric medium in the space between electrically conducting paths.

3. An electroluminescent article including a pair of spaced electrodes comprising at least a pair of electrically conducting paths forming continuous current paths between said electrodes, each of said conducting paths comprising substantially interconnected filaments, filaments from one of said paths being spaced from filaments of another conducting path; and electrolumenscent phosphor dispersed between spaced filaments.

References Cited UNITED STATES PATENTS 3,376,453 4/1968 Leach 3l3l08 2,755,406 7/1956 Burns 313108 2,837,660 6/1958 Orthuber et a1. 313108 X 2,887,601 5/1959 Bain 313108 3,148,107 9/1964 Selke 3l3-108 XR 3,290,537 12/1966 Logan 313-108 3,315,111 4/1967 Jaffe et al. 313108 JAMES W. LAWRENCE, Primary Examiner E. R. LA ROCHE, Assistant Examiner US. Cl. X.R. 250- 

